The invention relates more particularly to a fastener device for fastening a free turbine stator on a gas generator casing that shares a common axis with the turbine stator, the fastener device comprising a flange carrying a plurality of assembly parts (e.g. bolts) providing a first releasable connection between the turbine stator and the gas generator casing, the flange providing first centering of the turbine stator on the gas generator casing.
In certain aeroengine systems, e.g. an unducted fan (UDF) engine having two contrarotating propellers, the stator of the turbine carrying the propeller(s) is fastened on the structural casing of the gas generator. The turbine stator thus shares a common axis with the generator casing. It is preferable for the engine system to be a modular assembly, i.e. for the turbine stator to be removable so that it can be separated from and reassembled with the gas generator casing. The turbine can thus be separated from the gas generator for maintenance purposes, without it being necessary to disassemble the gas generator from the airplane, an operation that is burdensome and expensive. This makes it easier to maintain the free turbine.
The connection between the turbine stator and the generator casing is provided for example by means of an annular flange carrying a ring of bolts clamping the stator against the casing and holding it axially thereto. The flange is situated at one end of the stator. The flange is centered on the casing by its ring of bolts, and with the help of centering that is short, i.e. the flange is axially aligned with the casing with the additional help of the flange possessing a cylindrical annular outer surface that is slidably received in a cylindrical annular inner surface of the casing, the two cylindrical surfaces having the same radius about the common axis. The flange is thus engaged in the casing over a mutual engagement length that is equal to the size of said inner cylindrical surface of the casing along the common axis of the casing and the stator.
Nevertheless, for reasons of available space, convenience in assembly, and weight, the radius of the flange and the mutual engagement length are both limited. Unfortunately, the center of gravity G of the turbine 1 is situated about halfway between the flange and the other end of the turbine along the common axis, and is thus axially remote from the flange 20, as shown in FIG. 1. Since the weight of the turbine is large, there result large inertial forces due to accelerations and gyroscopic effects of the turbine, and also to vibration, thereby generating large amounts of torque on the flange. That torque can be sufficiently great to run the risk of breaking the connection via the flange by breaking bolts, or the risk of deforming the thin-walled structure of the turbine.
One way of avoiding the problem posed by that connection consists in using a turbine stator and a generator casing that constitutes a single part. Nevertheless, that loses the benefit of the turbine stator being modular relative to the generator, and the overall axial extent of the generator is longer.
The present invention seeks to remedy those drawbacks.